During his time at Indian River High School in Chesapeake, Virginia, he led the team to 51 straight victories and a state title his junior year (1987). As a senior he averaged 25 points, 15 rebounds and 12 blocked shots a game. He was named Player of the Year by USA Today, Parade, Gatorade, and Naismith. Mourning played college basketball for the Georgetown UniversityHoyas. He led the nation in blocked shots his freshman year and was an All-American his last year there.

Mourning was selected second overall in the 1992 NBA draft by the Charlotte Hornets, behind Shaquille O'Neal.[3] Mourning was named to the league's all-rookie team in 1993 after averaging 21.0 pts, 10.3 rebounds, and 3.47 blocks. He finished second to Shaquille O'Neal in rookie of the year voting.[4] He posted the highest scoring average of any rookie in Hornets history. Mourning and O'Neal were the first NBA rookies since David Robinson in 1989–90 to average 20 or more points and 10-plus rebounds in their first seasons. Mourning shattered Charlotte's blocked-shots records, becoming the Hornets' all-time career leader in the 49th game of the season. The greatest moment of Mourning's rookie season came on May 5, 1993 in Game 4 of a first-round playoff series against the Boston Celtics. His 20-footer at the buzzer gave the Hornets a 104–103 victory in the game and a three-games-to-one victory in the series. The Hornets lost in the second round to the New York Knicks in 5 games, with Mourning averaging of 23.8 points, 9.9 rebounds and 3.4 blocks in 9 playoff games. The following year, Mourning played in just 60 games, maintaining similar averages[quantify] in points, rebounds and blocks, but the Hornets missed the playoffs.

Mourning served as the centerpiece of the Pat Riley-coached Heat, and in his first season with the team he averaged 23.2 points, 10.4 rebounds and 2.7 blocks a game as Miami made the playoffs before being swept in the first round by the 72 win Chicago Bulls. Mourning played in the 1996 NBA All-Star Game and was joined by all-star point guard Tim Hardaway who arrived through a midseason trade.

The following year, the Heat won a franchise record 61 wins, second in the Eastern Conference to the defending champion Bulls, and Mourning averaged 19.8 points, 9.9 rebounds and 2.9 blocks. In the playoffs, Miami defeated the Orlando Magic in five games, and advanced to the conference semifinals against the New York Knicks, where the rivalry between the Heat and the New York Knicks intensified. The Knicks took a 3-1 lead in the series, but following a brawl between him and Charles Oakley, late in Game 5, in which multiple suspensions were handed down, Mourning scored 28 points in Game 6 followed by a 22-point, 12-rebound performance in Game 7 to help Miami advanced to the Eastern Conference Finals, a franchise first, to face Chicago. The Bulls took a 3-0 lead in the series, and Mourning guaranteed a victory in Game 4.[6] The Heat won the Game 87–80 but still lost the series in five games.

The next season, Mourning posted similar averages but only played in 58 games, and Miami was eliminated in the first round by the Knicks, a series in which Mourning was suspended for the 5th and deciding game due to an on-court fight with ex-teammate Larry Johnson, with Knicks Head Coach Jeff Van Gundy hanging onto Mourning's leg in an attempt to break it up.

The following season, Mourning averaged 21.7 points a game, 9.5 rebounds and 3.7 blocks a game, and won his second straight Defensive Player of the Year Award. Miami swept the Detroit Pistons in the first round of the playoffs, with Mourning dominating the Pistons[quantify]. The Heat faced New York, the fourth straight year that the two teams met in the postseason, and took a 3-2 series lead, but New York won the series in seven games. In the summer, Mourning and Hardaway won a gold medal with the United States at the Olympics in Sydney.

During the offseason, Miami underwent an overhaul and expectations leading up to the season were high.[citation needed] Prior the start of the 2000–01 season, however, Mourning was diagnosed with focal segmental glomerulosclerosis, a kidney condition, that caused him to miss the first five months of the season. He returned to play on March 27, and played a total of 13 games as Miami made the postseason but were swept in the first round by the Charlotte Hornets.

The following year, Mourning played in 75 games despite his kidney disease, and was selected to play in the 2002 NBA All-Star Game, where he scored 13 points off the bench. He averaged 15.7 points, 8.4 rebounds and 2.5 blocks a game, but the Heat missed the playoffs. As his condition worsened, Mourning did not play during the entire 2002–03 season and his expiring contract was not renewed by the Heat.

Mourning signed a four-year deal with the New Jersey Nets in 2003 as a free agent. But on November 25, 2003, Mourning retired from the NBA due to complications from his kidney disease. On December 19 of that year he underwent a successful kidney transplant. In 2004 he started practicing with the Nets again, and made the team's regular season roster during the 2004–05 season. He did not play a significant role with the Nets, however, and openly complained to the media that he wanted out of New Jersey, especially after the team traded away Kenyon Martin.[7] Mourning was traded to the Toronto Raptors on December 17, 2004. Mourning never reported to the Raptors, and was bought out of his contract at a remaining 9 million dollars on February 11, 2005. Raptors team officials later said that he did not meet the medical conditions to play for the team.[8][9] Mourning then finished the season with the Miami Heat being paid a second salary, the veteran's minimum.[10]

After being unhappy at the prospect of playing for a losing franchise,[citation needed] Mourning re-signed with the Heat on March 1, 2005. His role was reduced as a backup because of superstar Shaquille O'Neal, although he was called upon as a starter due to O'Neal missing stretches due to injury. O'Neal and Mourning even played together on the court at times, with Mourning playing power forward. Because of physical limitations, his minutes were reduced, but was still a steady contributor. Mourning's tenacious defense, steady offense, and all around hustle helped the Heat gain and maintain the second-best record in the NBA's Eastern conference during the 2004–05 season. Mourning finished the regular season ranking third in blocked shots at 2.66 per game, despite only playing 20 minutes per contest. Miami swept the Nets in the first round of the playoffs, with Mourning scoring 21 points with 9 rebounds in just 16 minutes in game 2. In the second round against the Washington Wizards, Mourning stepped in for the injured O'Neal and scored 14 points with 13 rebounds and 4 blocked shots in game 3 as Miami completed another four game sweep. Miami fell in seven games to the defending champion Detroit Pistons in the Eastern Conference Finals, with Mourning leading the team in blocks with 3 per game for the series.

Mourning re-signed with Miami, as the Heat once again re-hauled their roster, acquiring other veterans seeking a title such as Antoine Walker and Gary Payton. Mourning continued to serve as the Heat's backup center, and early on stepped in to serve as the team's starting center after O'Neal suffered an injury early on. Mourning started in 20 games out of a total of 65 games played, averaging 7.8 points and 5.5 rebounds while finishing third in the league with 2.7 blocks a game despite playing as a reserve. In the playoffs, Mourning continued to shine in his role as a defensive player off the bench, as Miami advanced past the Chicago Bulls and New Jersey before defeating Detroit in 6 games to advance to the 2006 NBA Finals, the first NBA Finals in franchise history and the first for Mourning. After a 2-0 deficit, Miami won all three of its home games led by the spectacular play of Dwyane Wade, and in game 6 in Dallas Mourning came off the bench to score 8 points with 6 rebounds and a team high 5 blocks to help Miami win its first NBA Championship in franchise history.

After winning the championship, Mourning announced that he would return to the Heat in 2006–07 to defend their title, despite receiving offers of more money from other teams, including the San Antonio Spurs. In 2007, Mourning announced he would return for one more year with the Heat and his 15th season. "It will definitely be my last year", Mourning said. After starting the season on a solid note averaging 6 points, 3.8 rebounds and 1.75 blocks in just over 16 minutes played per 24 games,[11] Mourning tore his patellar tendon in his right knee[12] on December 19, 2007, during the first quarter of a loss in Atlanta.[13][14] The injury, which occurred on the fourth anniversary of his successful kidney transplant, was said[who?] to be career-threatening, but rumors persisted[who?] about a return come the 2008–09 season, and Mourning himself said that this was not the way he wanted to end his career considering all he had been through already.

Mourning has averaged the most blocks in the NBA per 48 minutes with 5.46.

During the 2007–08 season, he became the Heat's all-time leader in points scored (which has since been surpassed by Dwyane Wade).

Mourning announced his retirement from the NBA on January 22, 2009. In his press conference he said, "I'm 38 years old and I feel like I have physically done all I can for this game."[citation needed] One month later, the Heat announced that they would retire Mourning's number 33 jersey, making him the first Heat player to be so honored.[15] The jersey retirement ceremony occurred on March 30, 2009, when the Heat hosted the Orlando Magic. During the extended halftime ceremony, Mourning was introduced by Florida Governor Charlie Crist; former Georgetown University basketball coach John Thompson; Basketball Hall of Famer Patrick Ewing; Heat players Dwyane Wade and Udonis Haslem; and Heat head coach Pat Riley.

In May 2009 he was named to the Hampton Roads Sports Hall of Fame, which honors athletes, coaches and administrators who contributed to sports in southeastern Virginia. In the following April, he was inducted into the Virginia Sports Hall of Fame in recognition of his outstanding high school, collegiate, and professional career as well as his commitment to volunteer service in the communities in which he has lived and worked throughout his life.[16]

Mourning announced his return to the Heat in late June 2009; he holds the position of Vice President of Player Programs and Development, which covers community outreach and mentoring young players.[17] On July 2014 the NBA announced that Mourning would be inducted into the Naismith Memorial Basketball Hall of Fame on August 8.

On November 25, 2003, Mourning's cousin and a retired U. S. Marine, Jason Cooper, was visiting Mourning's gravely ill grandmother in the hospital. Mourning's father was present and informed Cooper that Mourning was retiring that very same day from the NBA because of a life-threatening kidney disease, focal segmental glomerulosclerosis, the same problem that Sean Elliott had in 1999. Cooper asked if there was anything he could do, and began to contemplate donating one of his kidneys to his estranged cousin, whom he had not seen in 25 years and whom he only knew through basketball. Cooper was tested for compatibility, along with many other family members and friends (including fellow NBA center and good friend Patrick Ewing); during his grandmother's funeral, Mourning received the news that Jason Cooper was a match.

In 1997, Mourning established Alonzo Mourning Charities Inc. to aid in the development of children and families living in at-risk situations and provides support and services that enhance the lives of youth of promise.

After being diagnosed with focal glomerulosclerosis (FSGS), Mourning launched Zo's Fund for Life, a campaign which seeks to raise funds for research, education, and testing to fight focal glomerulosclerosis. Funds are allocated toward research for a cure, education for doctors and the general public, testing for early detection and a fund for those not able to afford medication.

In 2003 he also founded the Overtown Youth Center for underprivileged kids, located in Miami, Florida. The program aims to inspire, empower, and enrich these children while teaching them to become positive contributing citizens.

Mourning and his wife Tracy have three children: a son named Alonzo III ("Trey"), a daughter named Myka Sydney, and a second son named Alijah (born September 18, 2009).[22] They reside in Pinecrest, Florida, where Mourning purchased a two-story, 9,786-square-foot residence for $4.5 million in 2012.[23]

In July 2011 Mourning was sued by Miami-based lawyer Spencer Aronfeld on behalf of Alberto Candoleria for crashing his car into another car and then leaving the scene of the accident. The Florida Highway Patrol later charged Mourning with leaving the scene of a car accident. The accident allegedly occurred after he left Chris Bosh's wedding in Miami Beach after 3:00 A.M. Candoleria had just been in an accident when Mourning struck his car. He did not know if he was in his car when Mourning hit him as he claimed to have amnesia.[24][25][26]

In 2015 Mourning was one of eight Virginians honored in the Library of Virginia's "Strong Men & Women in Virginia History" for his charitable work and for his contributions to the sport of basketball.[20]